Discharge lamp having heat reflecting shields surrounding its electrodes



July 25, 1967 Q Rls ET AL 3,333,132

DISCHARGE LAMP HAVING HEAT REFLECTING SHIELDS SURROUNDING ITS ELECTRODES Filed May 19, 1964 INVENTORS Charles R. Edris and 40 Hugh D. Fraser. WVWVWWW Fi 7 BY ATTORNEY United States Patent 3,333,132 DISCHARGE LAMP HAVDIG HEAT REFLECTING SHIELDS SURROUNDING ITS ELECTRODES Charles R. Edris, Bloomfield, and Hugh D. Fraser, West Caldwell, N.J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed May 19, 1964, Ser. No. 368,471 3 Claims. (Cl. 31317) ABSTRACT OF THE DISCLOSURE An arc tube for a discharge lamp of the mercury-metallic iodide additive type has special metal caps carried over the arc tube end portions to act as heat traps. Each end cap has a portion bent into a ring-like form which fits about an end portion of the arc tube. Another portion of each end cap is formed as a series of adjacent, generally trapezoidal-shaped members connecting at their bases to the ring-like end cap portion, and the trapezoidal-shaped members are bent proximate their bases to conform to and cover over an end of the arc tube. A mat of refractory material is packed between each end cap and the portion of the arc tube which is covered by each end cap.

This invention relates to discharge devices and, more particularly, to high-pressure, vapor-discharge lamps of the so-called additive type.

It is known to modify high-pressure, mercury-vapor discharge lamps by including additive materials, and particularly selected metallic iodides, in the arc tubes. In the operation of such devices, the mercury, which is fully vaporized, usually establishes the proper loading or voltage drop across the lamp and the additive iodides improve the color and luminous output of the discharge. Such so-called additive lamps are generally disclosed in Illuminating Engineering Society, Paper 29, entitled Higher Efficiency Light Source Through the Use of Additives to Mercury Discharge, September 1962.

In order for such additive-type discharge devices to operate properly, it is necessary that the additive material be heated during operation to a high temperature so that it will have a relatively high vapor pressure. The vapor pressure of such additive material is normally controlled by the coolest portion of the arc tube, and this coolest portion will frequently occur at an end of the lamp, particularly when the arc tube is operated in a vertical position. It is also desirable to be able to efiiciently operate such additive lamps in any position.

It is the general object of this invention to provide a high-pressure, vapor-discharge lamp of the so-called additive type which operates with improved eificiency.

It is another object to provide a vapor-discharge lamp of the additive type wherein the cooler portions of the arc tube are heated in order to increase the vapor pressure of the additive material.

It is a further object to provide an additive-type discharge device which can be operated in any position without sacrificing efiiciency.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by positioning a refractory metallic retaining cap over each end of the arc tube, with each metallic retaining cap extending from each arc tube end and along the arc tube body a distance sufiicient to overlap substantially all portions of the electrode which is positioned proximate that respective end of the arc tube. Between each metallic retaining cap and the arc tube is packed a refractory fibrous material mat, with the material of which the mat is formed being non-gas-emitting, inert and non-reactive with respect to the arc tube and the metallic end caps at the operating temperatures of the arc tube. As a result, the heat which is generated proximate each electrode during operation of the device is entrapped at the ends of the arc tube, in order to inhibit condensation of the additive material filling at the end portions of the arc tube. As a result, the operation of the device is improved.

For a better understanding of the invention, reference should be had to the accompanying drawing wherein:

FIGURE 1 is an elevational view, partly in section, of a completed additive-type, high-pressure discharge lamp, with portions of the outer envelope broken away to show an end cap in detail;

FIG. 2 is an enlarged cross sectional view taken on the line IIH in FIG. 1;

FIG. 3 is a fragmentary, enlarged sectional view taken on the line III-III in FIG. 1 showing construction details of an end cap;

PIG. 4 is an enlarged sectional View taken on the line IVIV in FIG. 3, showing details for the mounting of an end cap;

FIG. 5 is a sectional view taken on the line VV in FIG. 4 illustrating a top plan view of an end cap;

FIG. 6 illustrates a refractory fiberous mat as is used for insulation between the end cap and the arc tube; and

FIG. 7 is a stamping showing one embodiment of an end cap before it is formed around an end portion of the arc tube.

With specific reference to the form of the invention illustrated in the drawing, the lamp. 10 in FIG. 1. is generally similar in construction to the usual high-pressure, mercury-vapor (HPMV) lamp, such as described in U.S. Patent No. 2,748,303, dated May 29, 1956 to Thorington, with the arc tube modified somewhat as described in detail hereinafter. The lamp 10 generally comprises a radiation-transmitting, sealed inner envelope or are tube 12 of quartz, polycrystalline alumina, or other suitable material, having operating electrodes 14 disposed proximate either end thereof and operable to sustain a vapor discharge therebetween. A charge of mercury 16 and a small amount of inert, ionizable starting gas, such as argon, are contained within the arc tube 12. The charge of mercury is present in predetermined amounts so that when the mercury is fully vaporized during operation of the lamp, the proper voltage drop across the lamp and the power input to the lamp will be realized.

As a specific example 117 mg. of mercury are included in the arc tube 12 which has a volume of 23.5 cc., a spacing betweenelectrodes of 62 mm., and an argon filling at a pressure of 2025 mm. Hg. Additive materials 18 which can be included in the arc tube include thallium iodide, sodium iodide and indium iodide, and other metallic iodides, chlorides or bromides can be used to supplement or replace these indicated additive materials, in order to obtain different discharge characteristics. Asa specific example, .thallium iodide can be included within the arc tube 12 in amount of 0.3 milligram per cc. of'total volume enclosed by the arc tube and sodium iodide can be included in amount of one milligram per cc. of volume enclosed by the arc tube. A small amount of additional thallium metal can also be included in the arc tube, if

desired. The are tube has a main body portion 12a of gentional starting resistor 28 to one of the lead-in connectors 24. The arc tube 12 is supported within the outer envelope 20 by a conventional supporting frame 30. In accordance with the present invention, and as clearly 'shown in FIGS. 1 through 5, a refractory'metallie re'- taining cap 32 is supported by a transverse supporting strap 34 over each closed end of the arc tube 12. Each metallic retaining cap 32, which is formed of nickel plated steel for example, extends from an arc tube sealed end 12b and along the are tube body 12a a distance sufficient to overlap substantially all portions of the respective ,electrode 14 which is positioned proximate the same end of the are tube 12. The overlapping positioning of the end cap 32 is shown more clearly in FIGS. 3 and 4. Between each end cap 32 and those portions of'the arc tube 12 which are covered by the end caps 32 is a tightly packed, refractory, fibrous material mat 36, shown in unwrapped form in FIG. 6. The mat 36 is formed of material which is non-gas-emitting, inert and non-reac- -tive with respect to the arc tube 12 and the metallic end caps 32 at the operating temperatures of the arc tube. As -a specific example, the mats 36 are formed of aluminum silicate fiber or quartz wool, and other suitable -material can be substituted therefor. In operation of the device, the end caps 32 and tightly packed mat 36 entrap heat generated proximate each of the electrodes 14 during operation of the device 10, .in order to inhibit condensation of the additive discharge-sustaining filling at the arc tube ends. p In one formof the invention, and as shown more clearly in FIGS.- 3, 4, and 7, the end caps 32 are supported in position by the transverse arc tube retaining straps 34. Each metallic end cap 32 comprises a first end cap portion 38 having a generally ring-like configuration and -encircling a portion of the body of the arc tube. A second ,end ,cap portion generally conforms to an end of the ,arc tube and is formed as a series of adjacent, generally trapezoidal-shaped members 40. The members 40 are con- Inected attheir respective bases to the ring-like end cap portion 38 and each of the trapezoidal-shaped members arebent proximate their base to generally conform to .i and cover over an end of the 'arc tube. While the end caps '32 could be formed as a continuous member, it is prefillustrated and described in detail, it is to be particularly electrically energizing said are tube, the improvement erable to form them as a strip of metal, such as is shown in FIG. 7, which strip of metal is bent to conform to the arc tube 12 and overlap itself.

In the operation of the additiveatype discharge devices 2 ,which incorporate the foregoingend caps 32 and mat 36 of refractory insulation, there is substantially no tendency for. anycondensation of additive discharge-sustaining material at the ends of the arc tube, irrespective of the operating position of the arc tube. This accordingly increases the vapor pressure of the additive discharge-sustaining material so that the lamps operate with improved efiiciency. t 3

It will-be recognized that the, objects of the invention have been achieved by providing an additive-type discharge lamp which operates with improved efliciency wherein the coolest. portions of the are tube are heated. .In addition, the discharge devicecan be operated in any .position Without sacrificing efficiency.

While a best embodiment of the invention has been understood that the invention is not limited thereto or thereby.

We claim:

1. In combination with a high-pressure arc-discharge device comprising, an elongated light-transmitting refractory arc tube having a main body of generally uniform diameter and closed at each end by a seal, said arc tube enclosing a predetermined charge of selected discharge-sustaining substance which is required to be maintained at a high tmperature for proper Operation of said device, electrodes operatively disposed within said arc tube proximate each end thereof and electrically conmeeting to lead-in conductors sealed through said are tube seals, a lightatransmitting outer envelope enclosing said arc tube, are tube support means within said outer envelope for engaging and supporting said are tube proximate the end seals thereof, and additional lead-in connections electrically connected to said are tube lead-in conductors and sealed through said outer envelope for which comprises:

(a) a refractory metallic retaining end cap over each.

closed end of said are tube, each said metallic end cap extending from an arc tube end and along the arc tube body a distance suflicient to overlap substantially all portions of the said electrodewhich is positioned proximate the same end of said arc tube to entrap heat generated proximate each said electrode during operation of said device, each said metallic end cap comprising a first portion having a generally ring-like configuration and encircling a portion of the body of said are tube and a second portion formed as a series of adjacent generally trapezoidal-shaped members connected at their bases 1 to said ring-like first portion and bent proximate their bases to generally conform to and cover over an end of said are tube; and

('b) a refractory fibrous material mat tightly packed between each said end cap and those portions of said are tube which are covered by said end caps, and

each said refractory mat being non-gas-ernitting, in-- 2. The discharge device as specified in claim 1, wherein 7 each said metallic end cap comprises a strip of metal bent to conform to said tube and overlapping itself at its ends.

3. The discharge device as specified in claim 1, wherein each said refractory mat is formed of aluminum silicate fiber or quartz wool.

References Cited UNITED STATES PATENTS JAMES w. LAWRENCE, Primary Examiner.

STANLEY D. SCHLOSSER, Examiner.

3/1943 Hays 313-25 X 

1. IN COMBINATION WITH A HIGH-PRESSURE ARC-DISCHARGE DEVICE COMPRISING, AN ELONGATED LIGHT-TRANSMITTING REFRACTORY ARC TUBE HAVING A MAIN BODY OF GENERALLY UNIFORM DIAMETER AND CLOSED AT EACH END BY A SEAL, SAID ARC TUBE ENCLOSING A PREDETERMINED CHARGE OF SELECTED DISCHARGE-SUSTAINING SUBSTANCE WHICH IS REQUIRED TO BE MAINTAINED AT A HIGH TEMPERATURE FOR PROPER OPERATION OF SAID DEVICE, ELECTRODES OPERATIVELY DISPOSED WITHIN SAID ARC TUBE PROXIMATE EACH END THEREOF AND ELECTRICALLY CONNECTING TO LEAD-IN CONDUCTORS SEALED THROUGH SAID ARC TUBE SEALS, A LIGHT-TRANSMITTING OUTER ENVELOPE ENCLOSING SAID ARC TUBE, ARC TUBE SUPPORT MEANS WITHIN SAID OUTER ENVELOPE FOR ENGAGING AND SUPPORTING SAID ARC TUBE PROXIMATE THE END SEALS THEREOF, AND ADDITIONAL LEAD-IN CONNECTIONS ELECTRICALLY CONNECTED TO SAID ARC TUBE LEAD-IN CONDUCTORS AND SEALED THROUGH SAID OUTER ENVELOPE FOR ELECTRICALLY ENERGIZING SAID ARC TUBE, THE IMPROVEMENT WHICH COMPRISES: (A) A REFRACTORY METALLIC RETAINING END CAP OVER EACH CLOSED END OF SAID ARC TUBE, EACH SAID METALLIC END CAP EXTENDING FROM AN ARC TUBE END AND ALONG THE ARC TUBE BODY A DISTANCE SUFFICIENT TO OVERLAP SUBSTANTIALLY ALL PORTIONS OF THE SAID ELECTRODE WHICH IS POSITIONED PROXIMATE THE SAME END OF SAID ARC TUBE TO ENTRAP HEAT GENERATED PROCIMATE EACH SAID ELECTRODE DURING OPERATION OF SAID DEVICE, EACH SAID METALLIC END CAP COMPRISING A FIRST PORTION HAVING A GENERALLY RING-LIKE CONFIGURATION AND ENCIRCLING A PORTION OF THE BODY OF SAID ARC TUBE AND A SECOND PORTION FORMED AS A SERIES OF ADJACENT GENERALLY TRAPEZOIDAL-SHAPED MEMBERS CONNECTED AT THEIR BASES TO SAID RING-LIKE FIRST PORTION AND BENT PROXIMATE THEIR BASES TO GENERALLY CONFORM TO AND COVER OVER AN END OF SAID ARC TUBE; AND (B) A REFRACTORY FIBROUS MATERIAL MAT TIGHTLY PACKED BETWEEN EACH SAID END CAP AND THOSE PORTIONS OF SAID ARC TUBE WHICH ARE COVERED BY SAID END CAPS, AND EACH SAID REFRACTORY MAT BEING NON-GAS-EMITTING, INERT AND NON-REACTIVE WITH RESPECT TO SAID ARC TUBE AND SAID METALLIC END CAPS AT THE OPERATING TEMPERATURES OF SAID ARC TUBE; WHEREBY DURING OPERATION OF SAID DEVICE EACH END PORTION OF SAID ARC TUBE COMPRISES AN EFFECTIVE HEAT TRAP TO INHIBIT CONDENSATION OF DISCHARGE-SUSTAINING FILLING AT THE END PORTIONS OF SAID ARC TUBE. 